Hydraulic system for actuating brakes



April 5, 1949, v F. c.. FRANK E1s-AL 2,466,224

I HYDRAULIC SYSTEEM FOR ACTUATING BRAKES Filed Aug. 50, 1944 2 Sheets-Sheet l @N j BY ATITUHNEY April 5, 1949. F. c. FRANK Erm. 24565224 HYDRAULIC SYSTEM FOR ACTUTING BRAKES Filed Aug. 30, 1944 2 Sheets-Sheet 2 /NVENTOIRS y Ey ATTUENEY Patented Apr. 5, 1949 f 2.466.224 l mimmo SYSTEM Fonacrva'rmc salinas Frederick 0.1mm: and william n. nu Bois. south a Bend, Ind..,assignors to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application August 30, 1944, Serial No. 551,838

Thisinvention relates to hydraulic systems for actuating brakes, and particularly to hydraulic systems which are used both to accomplish the ordinary service applications of the brakes and to set and hold the brakes for parking purposes.v

An object of the invention is to provide animproved hydraulic system for actuating brakes wherein means are provided for maintaining the brakes-applied during parking regardless of variations in Avolume of the fluid and wherein means are also provided for preventing the aforesaid means from having any efiect on the hydraulic system during normal service brake applications.

A further object of the invention is tov provide a hydraulic brake actuating .system having' the attributes mentioned in the preceding para'- graph, and additionally having means for pei-mitting an increased amount of fluid to be displaced from the master cylinder by pumping or multiplek stroking when' the brakes are tobe set` vfor parking. a

An important objectof the invention is to pro' I vide a parking brake which can be released by the simple expedient of building up pressure in the hydraulic system. This is particularly important in aircraft hydraulic braking systems, since the operaticn of the parking brakesr is selected'by means of a manually operated cable,. whichcan act-in one direction only. When-the operatorwishes to move the valves to positions lin which the brakes will be conditioned for park` ing, he exerts a pulling force on the cable. Since force cannot be exerted through the cablato movethe valves to non -parking position, other provisions must therefore be made for release of the brakes after parking.

A further objectof the invention is to'provide a braking system having the feature described in the lpreceding paragraph and also one or more of the other features heretofore listed. A still further object of the invention is to proventing operation of the parking brake holding 4 means, improved means for automatically locking: the fluid in the system whenever-the operator wishes to use the brakes for parking. i

Yet another object is to provide a single valve member which can select either service or parking brakes. When the service brakes are se lected, the lines between the master cylinder and the brake actuating motors are held open, and the'part of the system which is furnished for holding the brakes during parking is cut ofi -from the main system. On the other hand, when the parking brakes are selected, the parking part of ls claims. (ci, sol-54.5)

-nie system is in communication with ithe uuid lines, and also the means for automatically locking the iluid in the system is made operative.

A further object of the invention is to accomplish the several purposes and objects alluded to by means of an uncomplicated, light, and inexpensive structure. f'

Other objects and advantages of the invention will become apparent from the following description, reference being had therein to the accompanying drawings, in which:

Figure 1 is a section taken through a control for a hydraulic braking system, oi a type which incorporates our invention;v

Figure 2 is a section taken on the line 2-2 of .Figure-l.;-

Figure 31s a section taken on the vline 3-3 of Figure 2; and

i Figure 4 is a closeup or a portion of the structure shown in Figure 1. l

` The device shown in the several figures is 'adapted to act as a control for hydraulically ac` tuated brakes. 'I'his device is not only'arranged v 'to provide the customary service brake. applying 2'5v means, but also to provide sparking brake applying means-by permitting the fluid to vbe held under pressure in the lines.- This arrangement is lparticl'ilarly vadapted for moderny airplane.

braking systems. l

A vmaster cylinder bore |2which may be lo..

' cated ona vertical axis as shown, has the usual piston Il reciprocable therein. This piston is adapted to be drawn downwardly by means of'a manually operable rod i6, the rod actuating the vpiston by means yof an enlargement I8, which also .acts as a valve member controlling the` passage 20 through the piston. Whenthe rod I6' and piston I I are in released position, as shown,v valve member I8 -is unseated to permit communication of passage 20 with a reservoir chamber 22 above.

. the piston. If desired. this reservoir chamber 22 vide, in addition tothe means for `normally pre- `may be connected by means of passage 24' with another reservoir having a greater volume. The master cylinder may be' mounted on the body of the vehicle by any suitable means.

`The piston may be urged to released position by means of a return spring 28. and an additional spring 2l may normally bias the valve member I8 to open position, as shown. The usual seal 3l! is provided for the master cylinder piston.

Theoutlet of the master cylinder bore |'2 may be seen most vclearly in Figure 3, wherein it is shown connected by means of passage 3|`with a chamber 3,2, and the chamber 32 in turn communicates through passage 33 and ports 35 with ananas a chamber 34 (see Figures 1 and 4). Thecham' ber 34 ls in communication with the brake actuating motor or motors by means oi a port 36 (seen in Figure 2), and by means of the usual uid carrying conduit or conduits.

The normal or service brake applications are obtained by exerting a, force through rod I6 against piston I4, drawing the piston downwardly in bore I2 and displacing uid to the brake actuating motors to apply the brakes.

Since it is contemplated that the hydraulic system be also used as a means for holding the brakes applied when the vehicle is parked, means are provided for locking fluid in the system to hold the brakes applied when desired, and means are also provided for compensating for changes in the volume of the fluid during the time it remains trapped in the lines. 4

There are several reasons for providing means for compensating for changes in fluid volume during the time the fluid is trapped in the lines. In

case there is a certain amount of fluid loss due to leakage, it is necessary to have expansible means for maintaining pressure in the system. Likewise, if the iluid in the lines is hot at the time the brakes are first set for parking, and subsequently becomes considerably cooler, contraction of fluid will release the brakes, unless means are provided in the system for maintaining a Dressure. On the other hand, if the fluid is cool at the time the brakes are set for parking, and subsequently is heated considerably, the brakes would become locked unless a compressible medium were provided to allow the required expansion without building up an excessively high pressure It is also possible that the buildingof an excessively high pressure in the lines due to an expansion of the uid might injure some of the parts of the brake system.

Changes in volume of uid in the brake lines are particularly important where the hydraulic system is used to actuate airplane brakes. For example, the fluid may become hot to the point of boiling during a particularly severe stop after the plane lands, and' subsequently, particularly if the plane remains parked for a relatively long period, and the temperature cools considerably, the contraction of fluid in the lines will be quite noticeable. On the other hand, the fluid may become quite cold as the airplane is ying at a considerable altitude, and subsequently as the plane is landed and parked in a. region having a high temperature, the volume of fluid may be considerably expanded.

In order to compensate for such changes in fluid volume while the parking brakes are set, an

expansible chamber 38 is provided. Reciprocable in this chamber is a piston 40, which is loaded by a relatively heavy compression spring 42. If uid is forced into chamber 38 to move the piston 40 upwardly against the resistance of spring 42, energy will be' stored in the spring. Should the volume of iiuid in the system subsequently decrease, the pressure of the spring will maintain suiilcient pressure in the system to hold the brakes applied. On the other hand if the pressure against the spring should increase due to expansion of fluid in the system while the brakes remain applied, the spring 42 can be further compressed to compensate for such expansion.

Expansible chamber 38 is at times in communication with chamber 34l through passage 44 (see Figure 1). In the particular construction shown in the drawings, chamber 38 is connected to passage 44 by means of intersecting passages 46 and Although itv is desired to have an expansible chamber, such as chamber 38, which will compensate for changes in fluid volumewhlle the brakes remain set, thereare certain disadvantages in allowing free communication of the expansible chamber with the brake lines under all circumstances, as has heretofore usually been the case. During ordinary brake application there isno purpose to be served by forcing part of the fluid into the expansible chamber, and it has the disadvantage that part of the fluid displaced must be used in compressing the spring 42, and therefore performs no useful work in applying the brakes. This means, in effect. a loss of pedal travel.

Invorder to conserve pedal travel during normal or service braking operations, we have provided means for normally cutting oi expansible chamber 38 from the brake lines. This may be accomplished by blocking off passage 44. Although we do not intend to limit ourselves to such a construction, we nd it particularly convenient to utilize a single valve member both for blocking oil the expansible chamber during normal service brake applications, and for locking iiuid in the lines when the brakes are set for parking. To this end, we have provided a valve member 50 having seating surfaces 52 and 54 atopposite sides thereof. The seating surface 52 is adapted to close passage 44 and thereby cut off expansible chamber 38 from the fluid lines, which it will be remembered, are connected to chamber 34. The opposite seating surface 54 of valve member 58 is adapted to seat at 56 to cut off communication between the master cylinder bore I2 and chamber 34. A compression spring 58 exerts a force tending to move valve member 50 away from the mouth of passage 4e and toward seat 56.

However, a cam member 60 normally contacts an extension 62 of valve member 50 to hold the valve member in the position shown in Figures l and 4, in which it seats at the mouth of passage 44, while allowing communication between chambers 32 and 34. The cam member 60 is held in this position by means of a compression spring 54, which is sumciently effective to overcome spring 58. The relative effectiveness of springs 64 and 58 of course depends not only on the inherent force of the springs, but upon the mechanical leverage ratio of the mechanism between the springs.

The position of cam member 60 is under the control of the operator by means of rod B6, and lever 68 which is fulcrumed at 6l. end of the lever 68 is provided with an eye 10, by means of which it is connected to a cable 69. The cable 69 is a particularly satisfactory and inexpensive control for the lever 68. Usually the distance through which the control must extend on an airplane is considerable, and it is not feasible, to use a rod or other connection through which force can be exerted in both directions. Since the cable is operable only under tension, other means must be provided for returning valve member 50 and cam member 60 after they have been moved downwardly by the lever and cable.

When valve member 50 is in the position shown in Figures l and 4, expansible chamber 38 is cut off from the fluid lines, and free communication is permitted between master cylinder I2 and said iiuid lines, the iiuid being permitted to pass either toward or away from the master cylinder. The

The control master cylinder I2 returning to the master 5 l brakes are operated in the usual` manner by exerting a force on the master cylinder piston to apply a pressure in the brake actuating cylinders or motors and thereby stop the vehicle.

When the operator wishes to set the brakes for parking, he pulls the cable 89 which is connected to lever 88. thus forcing rod .68 in a direction to compress spring 64 and move cam member Bt out of the way of stem 62 of valve m'ember 50, thus permitting spring 58 to urge valve member Ell away from its seat at the mouth of passage 44 .and against seat 5S. Expansible' chamber $8 is now in communication with the brake lines. Furthermore, while fluid can be forced from past valve member into thebrake lines.- the fluid will be prevented from cylinder by said valve member B0, which now acts as a one-way check valve. If one stroke of piston I6 is not sutilcient to displace the necessary iiuid to the brakes, the operator may make as many strokes .with piston I4 as necessary, since the one-way check valve action of valve member 50, in effect, makes master cylinder I2 a pump capable of any number of strokes. On the return stroke of piston Il, fiuid'is drawn into master cylinder 'I2 past valve member I8, inthe usual manner. Then on the subsequent pressure stroke of piston Il this fluid is moved past valve 50 intothe brake lines, but due to the pressure of uid in the lines acting against valve member 50 to hold it seated at 56, the fluid cannot return to the master cylinder, and the brakes will remain set to hold the vehicle parked. When sumcient pressure is built up in the brake lines, it will act on valve member 50 with enough force to prevent cam member 60 from'returning to its original position, the spring 64 being maintained under pressure by valve member 50 acting through cam member 60. Consequently, longer exert any pressure on lever 68 to hold the cam member 60 out of the' way of valve stem 62. The brakes will now remain locked without any further attention from the operator, and the vehicle can be parked for an indefinite length of time. Should changes occur in the volume of fluid in the system, the spring 42 willv compensate for them inthe manner explained above. l

In order to release the brakes after the vehicle has been'parked, it is only necessary to actuate piston Il in mastercylnder I2 vto build up a pressure sufficient to counteract the pressure locked in the brakelines, thus permitting springy 64 to move the cam member 60 'back toward its original position and thereby lift valv'e member 5B from seat 56 and move it against the force of spring 58 toits original position, as shown in Figures 1 and 4.` As a matter of fact, it is not necessary to build up a pressure equal to the pressure locked in the lines-in order to release thebrakes, since the pressure created by the operator aids spring 6G in returning. cam member 6 0 and stem 62 to normal position. The pressure created in chamber 3.2 tendsto 'move cam'member 60 upwardly to move ste-m 62 and open valve 54, because the-cross-sectional area ofrod 66 the operator need no there is a definite advantage in being'able'to release them with less pressure.

` After the downward force exertedby the operator on rod I6 has been removed, uid will return from the brake lines to master cylinder I2,V and thence, if necessary, to the-reservoir. Il urthermore, check valve with respect to passage M. and therefore, fluid under the pressure of Ispring in chamber 38 is forced past valve member and back to master cylinder I2, the yspring l2 returning to the position shown in Figure 2, wherein piston I0 butts against the forward end of chamber 38.

From the foregoing description it is seen that the braking systemis conditioned for parking by exerting a pull through the cable 69, while the release is accomplished by building pressure in the bore I2. The structure iseilective and compact, n'ot only 'in the provision of the parking control means, but also in the single valve member which performs several functions. The expansible chamber is cut off from the brake lines during normal operation, and is only cut in for parking, at which time the fluid is trapped to prevent return to the bore I2.

Although a particular embodiment of our invention has been described. it will be understood by thoseskilled in the art that the object of the invention maybe attained by the use of constructions diierent in certain respects from that A disclosed without departing from the underlying principles of the invention. We therefore desire I by the following claims to include within the scope of our invention all such variations and modications by which substantially the results of our invention may be obtained through the use of substantially the same or equivalent` means.

We claim:

l. For use in a fluid pressure system having a pressure-actuated motor and a master cylinder operatively connected thereto, a fluid pressure trapping device comprising a rst valve means adapted to act at times as a one-way check valve permitting ow of fluid from the master cylinder to the motor but not inthe reverse direction, a

variable volume chamber capable of retaining under pressure the iiuid in the motor, a second motor and holds the second valve `means closed valve means adapted to control communication between the chamber and the motor, a control element which is'arranged to control both said first valve means and said second valve means and which in its released position holds the firstvalve means open to permit free ilow of fluid inboth directions between the master cylinder and to prevent communication between the motor and represents the area'differential between the lower the aforementioned chamber, said control element having a pressure responsive area which is acted on by the pressure of the master cylinder and. which is so arranged that the master cylinder pressure urges the Vcontrol element toward released position,v a first resilientmember arranged to open said second valve means and-move 'I said first valve means to the position'inrwhich it acts as a one-way check valve whenever the control elementA moves suiliciently from itsjeleased position, a second resilient member which urges the control element toward released position and which is capable of holding it there against the.

force of the vrst resilient member, and manually operable means for moving the ,control elementv away from its released'position.

2. A fluid pressure trapping devicejfor a-'iiuid' Pressure system comprising. a chamberforwrevalve member 50 now acts as a one-way www.

amasar taining iluid under pressure, a piston reciprocable therein, a spring acting on said piston to maintain pressure on the duid in the chamber, a iirst passage adapted to connect a uid pressure source with a iluid pressure operated motor, a second passage adapted to connect the aforementioned chamber with the fluid pressure operated motor, a valve member having seating surfaces on opposite sides thereof, one of which is adapted to seat at times against the mouth of the rst passage and the other oi.' which is adapted to seat at times against the mouth of the second passage, a spring acting on the valve member tending to move it away from the mouth of the second passage and against the mouth of the rst passage, a manually operable cam memlber comprising a frusto-condcal head formed on a rod, said frusta-conical head being adapted in normal position to compress said spring and hold the valve member away from the mouth -ot the iirst passage and against the mouth oi' the second passage, and a spring acting axially on said cam member with suiilcient strength to hold it inthe normal position except when manually developed mechanical force is exerted on the cam member or when a suilicient pressure urges the valve member. against the mouth of the first passage due to fluid pressure locked in the motor. the crossLsectional area of said rod being acted upon by the pressure developed at the pressure source to assist the last-mentioned spring in urging the cam member toward its normal position.

3. A fluid pressure trapping device for a uid pressure system comprising a chamber for retaining fluid under pressure, a piston reclprocable therein, a spring acting on said piston to maintain pressure on the iluid in the chamber, a ilrst passage adapted to connect a iiuld pressure source with a fluid pressure operated motor, a second passage adapted to connect the atorem'em tioned chamber with the fluid pressure operated motor, a valve member having seating surfaces on both sides thereof, one of which is adapted to seat at times against the mouth oi.' the'ilrst passage and the other of which is adapted to seat at times. against the mouth of the second passage, a spring acting on the valve member tending to move it away from the mouth o! the' second passage and against the mouth ot the rst passage, a manually operable rectilinearly movable cam member arranged in its normal position to compress said spring and hold the valve member away from the mouth of the rst passage and against the mouth of the second passage, and a spring acting on said cam member with sumcient strength to hold it in the normal position except when the manually developed mechanical force is exerted on the cam member or when a suillcient pressure urges the valve member against the'mouth of the first passage due to fluid pressure locked in the motor, said cam member having a pressure responsive area associated therewith which is acted upon by the pressure developed at the pressure source to assist the last-mentioned spring in urging the cam member toward its normal position.

FREDERICK C. FRANK. WILLIAM H. DU BOIS.

REFERENCES CITED UNITED STATES PATENTS Name Date Schnell June 15, 1943 Number Y 

